A radiation clinical thermometer has been proposed to measure a body temperature within a short period of time. This instrument is designed to perform noncontact measurement of the temperature of an eardrum selected as a measurement portion.
For example, such radiation clinical thermometer is disclosed in Japanese Unexamined Patent Publication No. 61-117422 wherein the head portion of the probe unit is inserted into the external acoustic meatus, and thermal radiations from the eardrum are focused to an infrared sensor by an optical waveguide placed in the head portion, thereby measuring the eardrum temperature. The probe unit with this infrared sensor includes a heating control means for preheating the head portion to a reference temperature (36.5.degree. C.). The head portion is preheated to a temperature near the body temperature, and calibration is performed in advance in this state. With this operation, when the head portion is inserted into the external acoustic meatus, the temperature of the head portion undergoes no change. For this reason, measurement errors caused by changes in the temperature of the head portion can be eliminated. That is, the inner surface of the optical waveguide must be set equal in temperature to that of the infrared sensor itself so as to prevent thermal radiations from the optical waveguide itself from causing measurement errors. In order to prevent a change in the temperature of the head portion upon insertion into the external acoustic meatus, the temperature of the head portion is stabilized at the reference temperature (36.5.degree. C.). With this setting, thermal radiations from the inner surface of the optical waveguide can be neglected.
The radiation clinical thermometer disclosed in Japanese Unexamined Patent Publication No. 61-117422, however, requires a heating control device with a high control accuracy. For this reason, the structure and circuit configuration of this instrument are complicated, and its size increases, resulting in an increase in cost. In addition, a long stabilization time is required to preheat the head portion and control its temperature to a constant temperature. Furthermore, high energy is required to drive the heating control device. This scheme cannot therefore be applied to a portable clinical thermometer using a compact battery as an energy source.
Under the circumstances, a radiation clinical thermometer with a high temperature measurement accuracy has been proposed, which is a compact, portable clinical thermometer having no heating control device. When the probe of this instrument is inserted into the external acoustic meatus to measure the eardrum temperature, the temperature of the probe changes. However, this change causes no error.
For example, such radiation clinical thermometer is disclosed in Japanese Unexamined Patent Publication No. 2-28524. Similar to the radiation clinical thermometer disclosed in Japanese Unexamined Patent Publication No. 61-117422, the radiation clinical thermometer disclosed in Japanese Unexamined Patent Publication No. 2-28524 uses an optical waveguide as an optical system for focusing thermal radiations from the eardrum. However, this instrument has no heating control device for the infrared sensor, and hence the infrared sensor and the optical waveguide are kept at almost the ambient temperature, i.e., room temperature. The first temperature sensor is arranged near the infrared sensor, and the second temperature sensor is arranged in the optical waveguide. A temperature is measured on the basis of the temperatures of the infrared sensor and the optical waveguide. If the difference in temperature between the infrared sensor and the optical waveguide is extraordinarily large, measurement is inhibited. If the temperature difference is smaller than a predetermined value, measurement is permitted in spite of the temperature difference. Body temperature data is then calculated in consideration of the temperatures of the infrared sensor and the optical waveguide. In this radiation clinical thermometer, an operation of calculating body temperature data is performed by a microcomputer on the basis of the output voltage from the infrared sensor, the output temperature from the first temperature sensor for measuring the temperature of the infrared sensor, and the output temperature from the second temperature sensor for measuring the temperature of the optical waveguide. When, for example, the probe is in the external acoustic meatus, the temperature of the optical waveguide gradually rises while the temperature of the infrared sensor hardly changes. For this reason, a temperature difference is caused between the infrared sensor and the optical waveguide. However, since body temperature data is calculated in consideration of these temperatures, an error caused by this temperature difference can be eliminated.
The following problems, however, are posed in the radiation clinical thermometer disclosed in Japanese Unexamined Patent Publication No. 2-28524. Since body temperature data is calculated by using a complicated equation based on a total of three variables, i.e., the temperature data obtained by the two temperature sensors and the output from the infrared sensor, the microcomputer requires a complicated program for this operation, and a long time for arithmetic processing. Furthermore, in the complicated equation used for this operation, constants such as the emissivity of the optical waveguide must be measured and set in advance. However, this setting is also difficult to perform.
The present applicant has disclosed a radiation clinical thermometer is Japanese Unexamined Patent Publication No. 6-142063, which uses an analog circuit to correct an error caused by the difference in temperature between first and second temperature sensors on the basis of the output voltage from an infrared sensor, the output temperature from the first temperature sensor adapted to measure the temperature of the infrared sensor, and the output temperature from the second temperature sensor adapted to measure the temperature of an optical waveguide.
The radiation clinical thermometer disclosed in U.S. Pat. No. 5,159,936 includes a first infrared sensor for receiving thermal radiations from the eardrum and thermal radiations from an optical waveguide itself, and a second infrared sensor for receiving only thermal radiations from the optical waveguide itself. This instrument is designed to correct an error caused by the difference in temperature between the optical waveguide and the infrared sensors by subtracting the output from the second infrared sensor from the output from the first infrared sensor.
Assume that the second temperature sensor is mounted on the probe unit of the radiation clinical thermometer disclosed in Japanese Unexamined Patent Publication No. 6-142063 to measure the temperature of the optical waveguide. In this case, the mounting positions of such sensors slightly vary with radiation clinical thermometers. For this reason, when the radiation clinical thermometer disclosed in Japanese Unexamined Patent Publication No. 6-142063 is mass-produced, the measurement results obtained by the respective radiation clinical thermometers include slight errors.
If the output from the second infrared sensor is simply subtracted from the output from the first infrared sensor, as in the radiation clinical thermometer disclosed in U.S. Pat. No. 5,159,936, a body temperature as a measurement result includes an error because of the influences and the like of a shielding plate for shielding the second infrared sensor from thermal radiations from an object to be measured.